# Make script executable (for unix systems)
$ chmod "a+x" cli.py 
# Run script (the unix way)
$ ./cli.py 
Hello, world
# Run script (the Windows way)
$ python cli.py
Hello, world
# Get help on the chmod program
$ man chmod
# Running the version of cli.py that lists the contents of sys.argv
$ ./cli.py 
0 ./cli.py
$ ./cli.py this is "some data" you know
0 ./cli.py
1 this
2 is
3 some data
4 you
5 know
# Running the version of cli.py that reads stdin as well (I flushed stdin with ctrl-d and killed the script with ctrl-c)
$ ./cli.py this is "some data" you know
0 ./cli.py
1 this
2 is
3 some data
4 you
5 know
first line
second line
third line
Read first line

Read second line

Read third line


^CTraceback (most recent call last):
  File "./cli.py", line 9, in <module>
    for i in sys.stdin:
KeyboardInterrupt
# Same version of cli.py, this time piping to stdin from echo (a simple program that prints the given text to stdout)
$ echo "hi there" | ./cli.py this is "some data" you know
0 ./cli.py
1 this
2 is
3 some data
4 you
5 know
Read hi there
# New version of cli.py -- does't print contents of sys.argv, does read from either a given filename or stdin (for the special case of filename == "-")
$ echo "hi there" | ./cli.py -
Read hi there

# Same version, printing itself
$ echo "hi there" | ./cli.py cli.py
Read #!/usr/bin/env python

Read 

Read import sys

Read 

Read if(__name__ == "__main__"):

Read     if(len(sys.argv) < 2):

Read         sys.stderr.write("Usage: "+sys.argv[0]+" -|input_filename\n")

Read     if(sys.argv[1] == "-"):

Read         myfile = sys.stdin

Read     else:

Read         myfile = open(sys.argv[1])

Read 

Read     for i in myfile:

Read         print "Read",i

Read 

Read 

# Same thing, trimming the extra newlines that print introduces
$ echo "hi there" | ./cli.py cli.py
Read #!/usr/bin/env python
Read 
Read import sys
Read 
Read if(__name__ == "__main__"):
Read     if(len(sys.argv) < 2):
Read         sys.stderr.write("Usage: "+sys.argv[0]+" -|input_filename\n")
Read     if(sys.argv[1] == "-"):
Read         myfile = sys.stdin
Read     else:
Read         myfile = open(sys.argv[1])
Read 
Read     for i in myfile:
Read         print "Read",i,
Read 
Read 
# Same thing, this time triggering the error message for no input file given (this is more useful than defaulting to stdin)
$ echo "hi there" | ./cli.py 
Usage: ./cli.py -|input_filename
# Same thing, the Windows way
$ python cli.py cli.py
Read #!/usr/bin/env python
Read 
Read import sys
Read 
Read if(__name__ == "__main__"):
Read     if(len(sys.argv) < 2):
Read         sys.stderr.write("Usage: "+sys.argv[0]+" -|input_filename\n")
Read         sys.exit(1)
Read     if(sys.argv[1] == "-"):
Read         myfile = sys.stdin
Read     else:
Read         myfile = open(sys.argv[1])
Read 
Read     for i in myfile:
Read         print "Read",i,
Read 
Read 
# Using "<" to redirect a file to stdin
$ ./cli.py - < cli.py
Read #!/usr/bin/env python
Read 
Read import sys
Read 
Read if(__name__ == "__main__"):
Read     if(len(sys.argv) < 2):
Read         sys.stderr.write("Usage: "+sys.argv[0]+" -|input_filename\n")
Read         sys.exit(1)
Read     if(sys.argv[1] == "-"):
Read         myfile = sys.stdin
Read     else:
Read         myfile = open(sys.argv[1])
Read 
Read     for i in myfile:
Read         print "Read",i,
Read 
Read 
# Also using ">" to redirect stdout to a file
$ ./cli.py - < cli.py > cli.txt
$ less cli.txt 
$ less cli.txt 
# Using "<< EOF" to pre-specify the contents
$ ./cli.py - << EOF
> Hello world
>   this
>   is some more text
> EOF
Read Hello world
Read   this
Read   is some more text
# Using the "<< EOF" trick as a text editor
$ cat > test.py << EOF
> #!/usr/bin/env python
> print "Hello world"
> EOF
$ chmod "a+x" test.py 
$ ./test.py 
Hello world
# Redirecting nothing to a file is a cute way to make a zero length file
$ > empty.txt